1. Field of the Invention
The invention relates generally to ground-based transport systems, and particularly to transport systems comprising vehicles which are magnetically lifted rather than mechanically lifted, and which are propelled magnetically while so lifted.
2. Description of the Related Art
The dramatic rise in urban and suburban populations, and the environmental and economic impacts that have accompanied such increases, have given new urgency to the development of a transportation technology that can transport large numbers of passengers rapidly, conveniently, economically, safely and reliably across distances as short as those of urban commuter lines or as long as transcontinental trips. A focus by transportation researchers in recent years has been the development of railway or guideway transportation systems as opposed to road or airborne systems. In particular, large efforts have been expended in recent years on the development of superconducting and non-superconducting magnetically levitated (lifted) train-like transport systems.
Most effort to date has focused on the concept of supporting a relatively conventional railway train by magnetic fields rather than by conventional steel wheels riding on steel rails. With large financial and technical support from their respective governments, Japanese and German research teams have expanded upon and developed experimental magnetic levitation (maglev) transportation research, some of which was pioneered in the United States. The research teams' respective implementations of magnetic levitation, however, differ greatly. For example, the Japanese system relies for lift upon the force which arises when strong electric currents, which are maintained in superconducting coils mounted within the cars, generate induced currents in a conducting guideway as the cars and coils associated therewith move along the guideway. The magnitude of this generated force is (roughly) inversely proportional to the separation distance between the coils and the guideway. Because the system is planned so far to operate in air like conventional railways, it is subject to aerodynamic drag, which increases power requirements and creates noise.
In the Japanese system, separation distances between the superconducting coils and the guide rails of the order of about 10 cm can be attained. Separation distances of this magnitude allow misalignments of the guide structure to be tolerated, because with large separation distances catastrophic contact between the cars and the guide structure are (other things being equal) less likely to occur than with closely-spaced systems.
A major difficulty with the Japanese system is that, as the superconductor currents once set cannot be changed moment to moment, the cars travel as though "floating" on soft springs whose spring constants and damping cannot be electronically controlled, rather than their oscillations being controlled and dampened by electronic feedback. An additional problem is that when transit speed drops below about 50 kph (the speed below which motion-induced lift generally ceases to be effective), auxiliary support apparatus such as landing wheels must be deployed in order to support the train.
In contrast to the Japanese transport system described above, the transport system which has been developed in Germany makes use of forces of magnetic attraction rather than repulsion. In the German system, conventional (i.e. non-superconducting) electromagnetic coils are positioned along lateral skirts of the rail cars and work to lift the rail cars toward a steel guideway positioned above the skirts of the rail cars. An advantage of this system is that it avoids the relatively advanced technology and the consequent capital and operating expenditures typically associated with superconductivity. However, the force of electromagnetic attraction is inherently unstable and requires sophisticated feedback control to ensure that the magnetic forces do not cause a car to come into contact with the overlying guideway. Because the linear density (kg/meter) of the German train is, like the Japanese train, relatively high, and magnets of conventional design can only provide the necessary strong forces without excessive power loss by using small rather than large air gaps, the clearance can only be of the order of about 1 cm. To ensure that the separation distance does not change above or below that optimal operating distance of about 1 cm during the course of vehicle operation, a highly nonlinear feedback system is required. The small separation and consequent tight tolerances in the guideway inherent in this system are reasons for concern as to its further development and its practical operating speed, as maintaining tight tolerances in the guideway is difficult. System operation is further complicated by environmental factors such as wind shifts, rainfall and debris, any or all of which are likely to be present occasionally and which can act to induce sudden, undesirable changes in vehicle position with respect to the guideway, in the worst case leading to physical contact.
Despite the foregoing system limitations, interest in magnetic levitation as a means for making better local and long distance terrestrial transport systems has increased over the years, as such transport systems should be capable of higher operating speeds and lower mechanical wear than conventional, wheel-on-rail transport systems. Furthermore, maglev systems even operating in the air are quieter than their conventional wheel-on-rail counterparts, and are therefore not as likely as conventional systems to meet with public opposition if proposed for location in urban areas.
As the current state of the art in magnetic levitation provides for the operation of such transport systems above ground, exposed to the surrounding environment, a principal limitation to the maximum operational speed of these transport systems has been aerodynamic drag and, as a separate point, noise. Such aerodynamic considerations have imposed a practical speed limitation of on the order of 500 kph for such transport systems, a speed which has also been reached, but only under experimental conditions by an unloaded train, in speed tests by a state of the art wheel-on-rail system, namely the French TGV-A system. The next operational TGV-A train is being built in France for an operating speed of about 300 kph. Clearly, wheel-on-rail technology is reaching its limits, because 2/3 of that speed was available for normally scheduled trains in the United States in the 1930's. Maglev systems depending on attraction, and therefore using small clearances, also would raise safety concerns if operating speeds were to be high.
In view of the foregoing limitations, an object and advantage of the present invention is to provide a high speed transport system that is safe, economical to build and operate, uses very little energy, provides for the transportation of large numbers of people and/or freight at higher speeds than are possible with conventional ground-based transportation systems, and is as far as possible environmentally benign. The present invention is also designed to occupy minimum width and to conform to existing rights of way, for example median strips on highways.
A further object and advantage of the subject invention is to provide a magnetically levitated transportation system which minimizes the exposure of the passengers transported thereby to magnetic fields used by the transport system in the course of its operation.
A further object and advantage of the invention is to provide a transport system that is closely and tightly controlled, yet provides a smooth ride, i.e., does not generate or transmit to passengers jarring forces.
Yet a further object and advantage of the invention is to provide a high speed transport system that is substantially isolated from aerodynamic and climatological influences and from acts of vandalism.
These and other objects and advantages of the subject invention will become apparent from a reading of the following detailed description and the accompanying drawing figures.